I have a table column that uses an enum type. I wish to update that enum type to have an additional possible value. I don't want to delete any existing values, just add the new value. What is the simplest way to do this?
253
votes
18 Answers
185
votes
NOTE if you're using PostgreSQL 9.1 or later, and you are ok with making changes outside of a transaction, see this answer for a simpler approach.
I had the same problem few days ago and found this post. So my answer can be helpful for someone who is looking for solution :)
If you have only one or two columns which use the enum type you want to change, you can try this. Also you can change the order of values in the new type.
-- 1. rename the enum type you want to change
alter type some_enum_type rename to _some_enum_type;
-- 2. create new type
create type some_enum_type as enum ('old', 'values', 'and', 'new', 'ones');
-- 3. rename column(s) which uses our enum type
alter table some_table rename column some_column to _some_column;
-- 4. add new column of new type
alter table some_table add some_column some_enum_type not null default 'new';
-- 5. copy values to the new column
update some_table set some_column = _some_column::text::some_enum_type;
-- 6. remove old column and type
alter table some_table drop column _some_column;
drop type _some_enum_type;
3-6 should be repeated if there is more than 1 column.
539
votes
PostgreSQL 9.1 introduces ability to ALTER Enum types:
ALTER TYPE enum_type ADD VALUE 'new_value'; -- appends to list
ALTER TYPE enum_type ADD VALUE 'new_value' BEFORE 'old_value';
ALTER TYPE enum_type ADD VALUE 'new_value' AFTER 'old_value';
70
votes
A possible solution is the following; precondition is, that there are not conflicts in the used enum values. (e.g. when removing an enum value, be sure that this value is not used anymore.)
-- rename the old enum
alter type my_enum rename to my_enum__;
-- create the new enum
create type my_enum as enum ('value1', 'value2', 'value3');
-- alter all you enum columns
alter table my_table
alter column my_column type my_enum using my_column::text::my_enum;
-- drop the old enum
drop type my_enum__;
Also in this way the column order will not be changed.
37
votes
If you fall into situation when you should add enum values in transaction, f.e. execute it in flyway migration on ALTER TYPE statement you will be get error ERROR: ALTER TYPE ... ADD cannot run inside a transaction block (see flyway issue #350) you could add such values into pg_enum directly as workaround (type_egais_units is name of target enum):
INSERT INTO pg_enum (enumtypid, enumlabel, enumsortorder)
SELECT 'type_egais_units'::regtype::oid, 'NEW_ENUM_VALUE', ( SELECT MAX(enumsortorder) + 1 FROM pg_enum WHERE enumtypid = 'type_egais_units'::regtype )
24
votes
Complementing @Dariusz 1
For Rails 4.2.1, there's this doc section:
== Transactional Migrations
If the database adapter supports DDL transactions, all migrations will automatically be wrapped in a transaction. There are queries that you can't execute inside a transaction though, and for these situations you can turn the automatic transactions off.
class ChangeEnum < ActiveRecord::Migration
disable_ddl_transaction!
def up
execute "ALTER TYPE model_size ADD VALUE 'new_value'"
end
end
16
votes
If you are using Postgres 12 (or later) you can just run ALTER TYPE ... ADD VALUE inside of transaction (documentation).
If ALTER TYPE ... ADD VALUE (the form that adds a new value to an enum type) is executed inside a transaction block, the new value cannot be used until after the transaction has been committed.
So no hacks needed in migrations.
UPD: here is an example (thanks to Nick for it)
ALTER TYPE enum_type ADD VALUE 'new_value';
12
votes
From Postgres 9.1 Documentation:
ALTER TYPE name ADD VALUE new_enum_value [ { BEFORE | AFTER } existing_enum_value ]
Example:
ALTER TYPE user_status ADD VALUE 'PROVISIONAL' AFTER 'NORMAL'
8
votes
Disclaimer: I haven't tried this solution, so it might not work ;-)
You should be looking at pg_enum. If you only want to change the label of an existing ENUM, a simple UPDATE will do it.
To add a new ENUM values:
- First insert the new value into
pg_enum. If the new value has to be the last, you're done. - If not (you need to a new ENUM value in between existing ones), you'll have to update each distinct value in your table, going from the uppermost to the lowest...
- Then you'll just have to rename them in
pg_enumin the opposite order.
Illustration
You have the following set of labels:
ENUM ('enum1', 'enum2', 'enum3')
and you want to obtain:
ENUM ('enum1', 'enum1b', 'enum2', 'enum3')
then:
INSERT INTO pg_enum (OID, 'newenum3');
UPDATE TABLE SET enumvalue TO 'newenum3' WHERE enumvalue='enum3';
UPDATE TABLE SET enumvalue TO 'enum3' WHERE enumvalue='enum2';
then:
UPDATE TABLE pg_enum SET name='enum1b' WHERE name='enum2' AND enumtypid=OID;
And so on...
7
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5
votes
I can't seem to post a comment, so I'll just say that updating pg_enum works in Postgres 8.4 . For the way our enums are set up, I've added new values to existing enum types via:
INSERT INTO pg_enum (enumtypid, enumlabel)
SELECT typelem, 'NEWENUM' FROM pg_type WHERE
typname = '_ENUMNAME_WITH_LEADING_UNDERSCORE';
It's a little scary, but it makes sense given the way Postgres actually stores its data.
5
votes
Updating pg_enum works, as does the intermediary column trick highlighted above. One can also use USING magic to change the column's type directly:
CREATE TYPE test AS enum('a', 'b');
CREATE TABLE foo (bar test);
INSERT INTO foo VALUES ('a'), ('b');
ALTER TABLE foo ALTER COLUMN bar TYPE varchar;
DROP TYPE test;
CREATE TYPE test as enum('a', 'b', 'c');
ALTER TABLE foo ALTER COLUMN bar TYPE test
USING CASE
WHEN bar = ANY (enum_range(null::test)::varchar[])
THEN bar::test
WHEN bar = ANY ('{convert, these, values}'::varchar[])
THEN 'c'::test
ELSE NULL
END;
As long as you've no functions that explicitly require or return that enum, you're good. (pgsql will complain when you drop the type if there are.)
Also, note that PG9.1 is introducing an ALTER TYPE statement, which will work on enums:
http://developer.postgresql.org/pgdocs/postgres/release-9-1-alpha.html
4
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3
votes
1
votes
Here is a more general but a rather fast-working solution, which apart from changing the type itself updates all columns in the database using it. The method can be applied even if a new version of ENUM is different by more than one label or misses some of the original ones. The code below replaces my_schema.my_type AS ENUM ('a', 'b', 'c') with ENUM ('a', 'b', 'd', 'e'):
CREATE OR REPLACE FUNCTION tmp() RETURNS BOOLEAN AS
$BODY$
DECLARE
item RECORD;
BEGIN
-- 1. create new type in replacement to my_type
CREATE TYPE my_schema.my_type_NEW
AS ENUM ('a', 'b', 'd', 'e');
-- 2. select all columns in the db that have type my_type
FOR item IN
SELECT table_schema, table_name, column_name, udt_schema, udt_name
FROM information_schema.columns
WHERE
udt_schema = 'my_schema'
AND udt_name = 'my_type'
LOOP
-- 3. Change the type of every column using my_type to my_type_NEW
EXECUTE
' ALTER TABLE ' || item.table_schema || '.' || item.table_name
|| ' ALTER COLUMN ' || item.column_name
|| ' TYPE my_schema.my_type_NEW'
|| ' USING ' || item.column_name || '::text::my_schema.my_type_NEW;';
END LOOP;
-- 4. Delete an old version of the type
DROP TYPE my_schema.my_type;
-- 5. Remove _NEW suffix from the new type
ALTER TYPE my_schema.my_type_NEW
RENAME TO my_type;
RETURN true;
END
$BODY$
LANGUAGE 'plpgsql';
SELECT * FROM tmp();
DROP FUNCTION tmp();
The whole process will run fairly quickly, because if the order of labels persists, no actual change of data will happen. I applied the method on 5 tables using my_type and having 50,000−70,000 rows in each, and the whole process took just 10 seconds.
Of course, the function will return an exception in case if labels that are missing in the new version of the ENUM are used somewhere in the data, but in such situation something should be done beforehand anyway.
1
votes
For those looking for an in-transaction solution, the following seems to work.
Instead of an ENUM, a DOMAIN shall be used on type TEXT with a constraint checking that the value is within the specified list of allowed values (as suggested by some comments). The only problem is that no constraint can be added (and thus neither modified) to a domain if it is used by any composite type (the docs merely says this "should eventually be improved"). Such a restriction may be worked around, however, using a constraint calling a function, as follows.
START TRANSACTION;
CREATE FUNCTION test_is_allowed_label(lbl TEXT) RETURNS BOOL AS $function$
SELECT lbl IN ('one', 'two', 'three');
$function$ LANGUAGE SQL IMMUTABLE;
CREATE DOMAIN test_domain AS TEXT CONSTRAINT val_check CHECK (test_is_allowed_label(value));
CREATE TYPE test_composite AS (num INT, word test_domain);
CREATE TABLE test_table (val test_composite);
INSERT INTO test_table (val) VALUES ((1, 'one')::test_composite), ((3, 'three')::test_composite);
-- INSERT INTO test_table (val) VALUES ((4, 'four')::test_composite); -- restricted by the CHECK constraint
CREATE VIEW test_view AS SELECT * FROM test_table; -- just to show that the views using the type work as expected
CREATE OR REPLACE FUNCTION test_is_allowed_label(lbl TEXT) RETURNS BOOL AS $function$
SELECT lbl IN ('one', 'two', 'three', 'four');
$function$ LANGUAGE SQL IMMUTABLE;
INSERT INTO test_table (val) VALUES ((4, 'four')::test_composite); -- allowed by the new effective definition of the constraint
SELECT * FROM test_view;
CREATE OR REPLACE FUNCTION test_is_allowed_label(lbl TEXT) RETURNS BOOL AS $function$
SELECT lbl IN ('one', 'two', 'three');
$function$ LANGUAGE SQL IMMUTABLE;
-- INSERT INTO test_table (val) VALUES ((4, 'four')::test_composite); -- restricted by the CHECK constraint, again
SELECT * FROM test_view; -- note the view lists the restricted value 'four' as no checks are made on existing data
DROP VIEW test_view;
DROP TABLE test_table;
DROP TYPE test_composite;
DROP DOMAIN test_domain;
DROP FUNCTION test_is_allowed_label(TEXT);
COMMIT;
Previously, I used a solution similar to the accepted answer, but it is far from being good once views or functions or composite types (and especially views using other views using the modified ENUMs...) are considered. The solution proposed in this answer seems to work under any conditions.
The only disadvantage is that no checks are performed on existing data when some allowed values are removed (which might be acceptable, especially for this question). (A call to ALTER DOMAIN test_domain VALIDATE CONSTRAINT val_check ends up with the same error as adding a new constraint to the domain used by a composite type, unfortunately.)
Note that a slight modification such as (it works, actually - it was my error)CHECK (value = ANY(get_allowed_values())), where get_allowed_values() function returned the list of allowed values, would not work - which is quite strange, so I hope the solution proposed above works reliably (it does for me, so far...).
0
votes
As discussed above, ALTER command cannot be written inside a transaction. The suggested way is to insert into the pg_enum table directly, by retrieving the typelem from pg_type table and calculating the next enumsortorder number;
Following is the code that I use. (Checks if duplicate value exists before inserting (constraint between enumtypid and enumlabel name)
INSERT INTO pg_enum (enumtypid, enumlabel, enumsortorder)
SELECT typelem,
'NEW_ENUM_VALUE',
(SELECT MAX(enumsortorder) + 1
FROM pg_enum e
JOIN pg_type p
ON p.typelem = e.enumtypid
WHERE p.typname = '_mytypename'
)
FROM pg_type p
WHERE p.typname = '_mytypename'
AND NOT EXISTS (
SELECT * FROM
pg_enum e
JOIN pg_type p
ON p.typelem = e.enumtypid
WHERE e.enumlabel = 'NEW_ENUM_VALUE'
AND p.typname = '_mytypename'
)
Note that your type name is prepended with an underscore in the pg_type table. Also, the typname needs to be all lowercase in the where clause.
Now this can be written safely into your db migrate script.
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